For various logistical and technical reasons, concrete floors are typically made up of a series of individual cast-in-place concrete blocks or slabs referred to herein as “concrete slabs” or “slabs”. These concrete slabs provide several advantages including relief of internal stress due to curing shrinkage and thermal movement. However, there are various known issues with such concrete slabs. These issues often involve the joint between concrete slabs, or the interface where one concrete slab meets another concrete slab.
More specifically, freshly poured concrete shrinks considerably as it cures or hardens due to the chemical reaction that occurs between the cement and water. As the concrete shrinks, tensile stress accumulates in the concrete. Therefore, the joints need to be free to open and thus enable shrinkage of each of the individual concrete slabs without damaging the concrete floor. The joint openings create discontinuities in the concrete floor surface that can cause the wheels of a vehicle (such as a forklift truck) to impact the edges of the adjacent concrete slabs that form the joint and chip small pieces of concrete from the edge of each concrete slab, particularly if the joint edges are not vertically aligned. This damage to the edges of concrete slabs is commonly referred to as joint spalling. Joint spalling can interrupt the normal working operations of a facility by slowing down forklift and other truck traffic, and/or causing damage to trucks and the carried products. Severe joint spalling and uneven joints can cause loaded forklift trucks to overturn (which of course is dangerous to people in those facilities). Joint spalling can also be very expensive and time consuming to repair.
Joint edge assemblies that protect such joints between concrete slabs are widely used in the construction of concrete floors (such as concrete floors in warehouses). Examples of known joint edge assemblies are described in U.S. Pat. Nos. 6,775,952 and 8,302,359. Various known joint edge assemblies enable the joint edges to both self-open with respect to the opposite joint edge as the adjacent concrete slabs shrink during curing or hardening. One known joint edge assembly is generally illustrated in FIGS. 1, 2, and 3. This known joint edge assembly 10 includes two separate elongated joint edge members 20 and 40 temporarily held together by a plurality of connectors 60. The connectors 60 connect the elongated joint edge members 20 and 40 along their lengths during installation. This known joint edge assembly 10 further includes a plurality of anchors 22 that extend from the elongated joint edge member 20 into the region where the concrete of the first concrete slab 90 is to be poured such that, upon hardening of the first concrete slab 90, the anchors 22 are cast within the body of the first concrete slab 90. This known joint edge assembly 10 further includes a plurality of anchors 42 that extend from the elongated joint edge member 40 into the region where the concrete of the second concrete slab 96 is to be poured such that, upon hardening of the second concrete slab 96, the anchors 42 are cast within the body of the concrete slab 96. This known joint edge assembly is positioned such that the ends or edges of the concrete slabs are aligned with the respective outer surfaces of the elongated joint edge members. FIGS. 1 and 2 illustrate the joint edge assembly 10 prior to installation and before the concrete is poured, and FIG. 3 illustrates the joint edge assembly 10 after installation and after the concrete slabs have started shrinking such that the elongated joint edge members 20 and 40 have separated to a certain extent.
Another issue with such joints involves the vertical movements of adjacent concrete slabs relative to each other. The concrete slabs (such as concrete slabs 90 and 96) are preferably configured to move individually, and are also preferably configured with load transferring devices to transfer loads from one concrete slab to the adjacent concrete slab. Transferring loads between adjacent concrete slabs has been accomplished using various different load transferring devices. For example, certain known load transferring devices are in the form of steel dowels or rods and dowel receiving sheaths having circular cross-sections (such as those disclosed in U.S. Pat. Nos. 5,005,331, 5,216,862, and 5,487,249). Other known load transferring devices are in the form of steel dowels or rods and dowel receiving sheaths having rectangular cross-sections (such as those disclosed in U.S. Pat. No. 4,733,513). Such circular and rectangular dowels are capable of transferring loads between adjacent concrete slabs, but have various shortcomings. For example, if such circular or rectangular dowels are misaligned (i.e., not positioned perpendicular to joint), they can undesirably lock the joint together causing unwanted stresses that could lead to slab failure in the form of cracking of the concrete slab. Such misaligned dowels can also restrict movement of the concrete slabs in certain directions. Another shortcoming of such circular and rectangular dowels is that they typically enable the adjacent slabs to move only along the longitudinal axis of the dowel. Another known shortcoming of such circular and rectangular dowels results from the fact that, under a load, only the first 3 to 4 inches of each dowel is typically used for transferring the load from one slab to the adjacent slab. This can create relatively high loadings per square inch at the edge of one or more of the adjacent concrete slabs, which can result in failure of the concrete above or below the dowel.
To solve these problems, load transferring devices such as the dowel and dowel receiving sheath disclosed in U.S. Pat. No. 6,354,760 were developed. These known load transferring devices provide increased relative movement between the adjacent concrete slabs in a direction parallel to the longitudinal axis of the joint and reduce loadings per square inch in the adjacent concrete slabs close to the joint, while transferring loads between the adjacent concrete slabs. These load transferring devices are commercially sold by the assignee of the present application. These load transferring devices have been widely sold and commercially utilized.
In certain circumstances, such as under heavy loads or in relatively thin concrete slabs, it has been found that these load transferring devices do not always move into or remain in or close to the optimal position for load transfer between the adjacent concrete slabs after the adjacent concrete slabs cure. FIGS. 4A, 4B, 5A, and 5B illustrate this issue. FIGS. 4A and 4B show two adjacent cast-in-place concrete slabs 90 and 96 before such concrete slabs 90 and 96 have substantially cured and separated, and with the dowel 70 and the dowel sheath 80 of U.S. Pat. No. 6,354,760. FIGS. 4A and 4B show the dowel 70 positioned half way in the dowel sheath 80 for installation. The central or widest area of the dowel 70 is adjacent to the central plane 98 between the slabs at this point. FIGS. 5A and 5B show a subsequent point in time when the two adjacent cast-in-place concrete slabs 90 and 96 have cured and separated (or have otherwise moved with respect to each other) and that have been formed with the dowel 70 and dowel sheath 80 of U.S. Pat. No. 6,354,760. FIGS. 5A and 5B show the dowel 70 positioned further in concrete slab 96 than in concrete slab 90, and that the central or widest area of the dowel 70 is not positioned along or adjacent to the central plane 98 between the separated concrete slabs 90 and 96. FIGS. 5A and 5B thus show that this known dowel 70 can move relative to both concrete slabs 90 and 96 and can often be positioned offset from the optimal position for load transfer between two adjacent cast-in-place concrete slabs.
In certain circumstances, it has also been found that these known load transferring devices 70 and 80 can cause stress fractures to the concrete slabs or parts of the concrete slabs.
Accordingly, there is a need for improved load transfer devices and methods of using such improved load transfer devices that solve these problems.